Balanced capillary ink jet pen for ink jet printing systems

Abstract

This application is directed to an ink jet pen having an ink supply housing which includes a primary ink reservoir (30) and a secondary ink reservoir (26). A balancing capillary member is positioned within the ink supply housing and includes ink flow path (20, 24) which extends between the primary ink reservoir (30) and the secondary ink reservoir (26). This capillary member is operative to draw ink from the primary ink reservoir (30) and into or toward the secondary ink reservoir (26) by capillary action as temperature and pressure within the primary ink reservoir increases. Conversely, when temperature and pressure in the housing decreases, ink will be drawn back into or toward the primary ink reservoir (30). In addition, the primary ink reservoir (30) is connected by way of a suitable ink feed path to an ink jet printhead (32) for supplying ink to the printhead during an ink jet printing operation.

We claim: 
     
       1. A method for controlling backpressure in an ink jet pen which includes: a. providing primary and secondary ink reservoirs in a pen body housing,   b. providing ink in said primary reservoir and maintaining said ink at a controlled pressure,   c. providing an open ink flow path between said primary and secondary reservoirs, and   d. flowing ink back and forth through said open ink flow path between said reservoirs in response to variations in ambient temperature and changes in pressure above the liquid surface of said ink, whereby ink may be supplied from said main ink reservoir to an ink jet printhead at a substantially constant backpressure over a   
     
     
       2. The method defined in claim 1 wherein the flowing of ink back and forth between reservoirs includes introducing air bubbles into said primary ink reservoir from a capillary ink flow path thereto, whereby pressure regulation in said primary reservoir is maintained by a combination of bubble formation therein and the surface tension and capillary action of ink in said capillary ink flow path. 
     
     
       3. An ink jet comprising: a. an ink supply housing having a primary ink reservoir and a secondary ink reservoir therein,   b. a balancing capillary member positioned adjacent to or within said ink supply housing and including an open ink flow path extending between said primary ink reservoir and said secondary ink reservoir and operative to draw ink from said primary ink reservoir and into or towards said secondary ink reservoir by capillary action with changes in pressure above the ink within said primary ink reservoir, and   c. means interconnecting said primary ink reservoir to an ink jet printhead for supplying ink to said printhead during an ink jet printing operation.   
     
     
       4. The ink jet pen defined in claim 3 wherein said balancing capillary member is positioned adjacent openings to both of said primary and secondary ink reservoirs and includes an ink flow path therein which extends from an ink feed port in said primary ink reservoir to an ink feed port in said secondary ink reservoir. 
     
     
       5. The ink jet pen defined in claim 4 wherein said balancing capillary member further includes a main ink distribution path extending between said main ink reservoir and a printhead support surface and an ink overflow path extending between said secondary ink reservoir and the outside ambient. 
     
     
       6. The ink jet pen defined in claim 5 wherein said printhead is a thin film printhead mounted on said support surface and is fed ink by a path extending directly to said primary reservoir. 
     
     
       7. In an ink jet pen having a pen body housing with a primary ink reservoir therein for storing ink and a printhead with ink ejection means mounted on or in said housing and operative to receive ink from said primary ink reservoir during an ink jet printing operation, the improvement characterized in that said housing further includes a secondary reservoir and means including an open capillary path for flowing ink back and forth between said primary reservoir and said secondary reservoir as a function of changes in pressure above the surface of ink stored in said primary reservoir. 
     
     
       8. The pen defined in claim 7 wherein said secondary reservoir is a tubular shaped feed path which extends from said primary reservoir to the outside ambient. 
     
     
       9. The pen defined in claim 7 wherein said secondary reservoir is separated from said primary reservoir and said flowing means is a non-linear capillary tube connecting said primary and secondary reservoirs. 
     
     
       10. The pen defined in claim 9 wherein said non-linear capillary tube is formed in a capillary section of said housing and is positioned directly between openings in said primary and secondary reservoirs for passing ink therebetween. 
     
     
       11. The pen defined in claim 7 wherein said secondary reservoir is separated from said primary reservoir and is connected thereto by means of a capillary tube. 
     
     
       12. The pen defined in claim 11 wherein said secondar reservoir is situated beneath said primary reservoir and is connected thereto by a capillary tube. 
     
     
       13. The pen defined in claim 12 wherein said secondary reservoir contains an air vent tube which extends to the outside ambient. 
     
     
       14. The pen defined in claim 13 wherein a separate ink well is formed around the opening of said straight capillary tube into said primary reservoir to enhance air bubble formation in said primary reservoir as it is being depleted of ink. 
     
     
       15. A device for maintaining a substantially constant backpressure in an ink jet pen which comprises: a. primary and secondary ink reservoirs in a pen body housing and an ink ejection printhead mounted on or in said housing, and   b. means interconnecting said primary and secondary reservoirs for drawing ink by capillary action into or toward said secondary reservoir from said primary reservoir when the pressure above the liquid surface in said primary reservoir is increasing and further for returning ink into or towards said primary reservoir from said secondary reservoir when the pressure above the liquid surface in said primary reservoir is decreasing, whereby the backpressure at the ink ejection printhead of said device is maintained substantially constant over a given temperature range.   
     
     
       16. A method for controlling backpressure in an ink jet pen which comprises the steps of: a. providing a controlled pressure above an ink surface in the primary reservoir of an ink jet pen,   b. providing a secondary ink reservoir for said pen,   c. providing an open ink flow conduit between said primary and secondary reservoirs,   d. flowing ink by capillary action from said primary reservoir and through said conduit and to or toward said secondary reservoir when the pressure above said ink surface in said primary reservoir is increasing, and   e. flowing ink through said conduit and to or toward said primary reservoir when the pressure above said ink surface in said primary reservoir is decreasing.